Current limited



Jan. 9, 1934.

D. L. KEISER 1,943,021

CURRENT LIMITER Filed May 8, 1931 2 Sheets-Sheet l D. L. KEISER CURRENT LIMITER Jan. 9, 1934.

Filed May 8, 1931 2 Sheets-Sheet 2 a I a a f //////7 Patented Jan. 9, 1934 PATENT, OFFICE UNITEDQSTATES 5 Claims.

My invention relates to controlling devices for electric current and particularly to what are known as current limiters for controlling the amount of current taken by a consumer. Where I house circuits or consumption circuits are provided with metering devices a somewhat wide margin is usually allowed between maximum and minimum current consumed, and the only limiting devices required are protective devices such as fuses or automatic cut-outs, which are intended merely toprotect the circuits themselves and the apparatus connected thereto from damage due to excessive current flow." There are cases however where it is necessary to make a contract for a certain maximum amount of current; and in such cases'it sometimes happens that a dishonest or careless person may exceed the limit if only ordinary switching and control means are provided. In some jurisdictions where such conditions exist, the specifications for current limiters are'very severe. For example one government agency requires limiters to operate on a short circuit without injury to the contacts; also to operate with only 2% variation in load due to temperature changes from 20 to centigrade, and also not to have more than three volts drop across the terminals of each element when carrying full load. 1

It is the object of my present invention to meet 30 these and other conditions and to provide an automatic current limiter which will absolutely and automatically prevent the theft or use of excess current beyond a predetermined amount, which will be simple to operate and keep in rev pair, and which will be effective even if a short circuit is placed between terminals.

I attain my object byproviding a double pole limiter with one concentric cable and a plurality of house or consumption circuit leads. The cir- 401 cuit is normally closed through a pair of contacts mounted on thermostatic bars and a pair of cooperating contacts mounted on spring strips which in turn are mounted through insulators upon thermostatic brackets which respond to changes in temperature to keep the contacts so adjusted as to compensate therefor, whereby the amount of current required to operate the device ismaintained constant. The springs are mounted between tension devices so as to be subject to a 60 compression strain, whereby they require to be forced past center in both directions. The first pair of thermostatic bars carrying contacts are provided with heating coils which'are included in the circuit. An increased flow of current bev6 yond the normal in these coils will heat the thermostatic bars and lift up the springs carrying the companion contacts until they snap past center and suddenly open the circuit. This remains open until the thermostatic bars cool and retract, whereupon they pull the springs down by means of over-hanging insulated fingers, until the springs again snap past center and close the circuit. 7

The thermostatic bars are adjustable by means which will be presently described and claimed herein and the entire combination operates in such manner as to meet the most severe requirements such as those mentioned above.

My invention is illustrated in the accompanying drawings, in which Fig. 1 is a plan view of the complete assembly of my current limiter enclosed in a case from which the top has been removed.

Fig, 2 is a sectional view on the line 2-2 of Fig. 1.

Fig. 3 is a similar sectional view on the line 3--3 of Fig. 1.

Fig. 4 is a circuit diagram showing the application of my limiter to two-wire feeder circuits and house circuits of the type employed in the United States.

Fig. 5 is a similar diagram showing the limiter applied to a polyphase circuit of the type employed in some localities in the United States and in some foreign countries.

Referring first to Figs. 1 and 2, 1 is a box which may be of aluminum in which the limiter proper is mounted with an entrance box 1a containing a terminal board which will be presently described. The limiter propercomprises the following instrumentalities: two bimetallic thermostatic bars or elements 2 and 2a respectively extend from opposite sides of the box to the center, where they carry contacts 13 and 13a shown in Fig. 2 cooperating with contacts 14 and 14a carried on two springs 3 and 3a, which extend from side to side of the box at right angles to the thermostats 2 and 2a, having their ends mounted on self-adjusting supports 9 and 9a carried on two thermostatic bars 6 and 6a. The bars 6 and 100 6a are sensitive to temperature changes and by their expansion and contraction automatically adjust the position of the thin metal strips 9 and 9a carrying the springs 3 and 3a and the contacts carried thereby accordingto the tempera- 105 ture ofthe surrounding air. Each of the thermostats 6 and 6a is securely fastened to the base of the box at one end, and the other end is riveted to the thin metal strip 9 or 9a carrying the spring support or yoke 5 or 5a. With this arthe contacts 13 and 14, and 130;

rangement, the same amount of electricity is required to trip the spring at 20 Centigrade as is required at 45 Centigrade. The primary function of the springs 3 and 3a as such is to produce an instantaneous opening or closing of the contacts l3 and 14 and 13a and 14a. For this purpose the supports 9 and 9a are mounted on yokes and 5a the ends of which are connected together by means of tension rods 4 and 4a. The yokes are bored at their ends to pass the ends of the tension rods, which are threaded to receive adjusting and lock nuts 4?). By setting up these nuts, the springs 3 and So can be placed under compression so that in order for their metal points to be either raised or lowered to the limit of their travel they must be snapped past center in a manner Well understood by those skilled in the art. Mounted upon the thermostatic bars 2 and 2a are metal arms and 15a which extend upward and have their ends turned out over the springs 3 and 3a respectively. The upper end of the arm 15 carries a screw 16 having a button of insulation so as to mechanically engage the upper side of the spring 3 without effecting electrical connection therewith. Similarly the arm 15a carries on its end a screw 16a with a button of insulation inserted in its tip so as to engage the upper side of the spring 3a. When the springs 3 and 3a are in the lowermost position with the contacts l3-14 and 13a 14a engaging each other, the buttcn tips of the screws 16 and 16a are approximately 3/1000 of an inch above the springs. When the thermostatic bars 2 and 24: rise, they push up the contacts and thereby push up the springs 3 and 3a until the latter suddenly snap past center. Thereafter the springs are in their uppermost position and rest against the buttons of insulation in the screws 16 and 16a, while the contacts 13 and 14, and 13a and 145: are open. lhe total spring travel with the thermostatic element removed, is approximately 5% of an inch. When the thermostatic bars cool off and move downwardly, they pull down the arms 15 and 15a and thereby bring pressure to bear on the upper side of the springs 3 and 3a through the screws 16 and 16a and the insulating buttons in their tips. This continues until the springs reach center, when they snap the rest of the way down instantaneously closing and 14a, leaving the screws 16 and 16a separated from the springs, which are then again in their lowermost position.

The mounting of the thermostatic bars comprises a block of fibre insulation 12 fastened to an adjusting base 8 supported on a forwardly extending leg 8a, screws 10 and 10a and 11 and 11a. Screws 11 and 11a are used as jack screws for lifting the rear and outer end of base 8, which will in turn lower the contact carried by the thermostat 2. When the correct position has been reached, screws 10 and 100 are set up and fastened by means of lock nuts or other suitable means 101). This arrangement gives a. very accurate adjustment. Each thermostatic bar 2 or 2a is provided with a heating coil 7 or 7a underlying the bar and secured to it in any suitable manner. The outer ends of these heating coils are connected by conductors 7b and 7c and the terminals 1'7 and 18 on the terminal rack 19. Mounted upon each sp 'ng 3 or 3a is a sleeve 3c or 3d. These sleeves c and 3d carry at their inner ends the contacts 14 and 14a and at their outer ends are connected to the conductors 20 and 21 extending to terminals 22 and 23 on the v terminal rack 19. The metalof the sleeves is heavy enough to form a. good conductor without heating so as to affect the spring tension. It will be understood that the screws 16 and 16a overlie these sleeves in line with the contacts beneath the same.

In the entrance box, the external conductors 24 and 25 pass from the terminals 17 and 18 to form a concentric cable. This concentric cable consists of thewire 24 having around it insulating material 24a, and around this insulating material is the other conductor 25, which is also insulated and grounded as shown in the circuit diagram, Fig. 5. This is to prevent a thief from tapping the inside wire between the limiter and the circuit to which it is connected. The other two terminals 22 and 23 are connected by external conductors or leads 26 and 27 to the house or consumption circuit.

The arrangement thus described forms a double pole limiter by the use of which, if a short circuit is placed between the outer circuit of the concentric cable and the house wire of the same circuit, it will short circuit one of the interrupters of the limiter, but the other one con; nected to the inside wire of the concentric cable will open the circuit in case the consumer takes more load than contracted for. v

The thermostats 2 and 2a are bimetallic, the upper side of each being made of steel and the lower of brass. When this material is heated by the resistance coils 7 or 7a mounted underneath the strap, it raises the contact springs 3 and 3a slightly, without breaking; but if an overload of current be introduced, the additional heat due thereto warps the thermostat to a point where it raises the contacts (13 and 14 or 130 and 14a) to the tripping point. The spring then snaps upwardly past center and opens the circuit, interrupting the service until the thermostat 2 or 2a has cooled sufliciently for the insulated screw on top to bring the spring backto normal position. The circuit is very quickly interrupted and also quickly closes, preventing burning of the contacts.

Referring to Fig. 4, the casing 1 is shown in outline only with the terminal rack 19 exposed. From the terminal rack wires 24 and 25 lead to the incoming supply circuit 30-31; while the conductors 26 and 27 lead to the house or consumption circuit on which are shown typical translating devices 32. Any overload, beyond the predetermined limit, on the circuit 26-27 causes overheating of the thermostatic bars 2 and 2a, and results in opening the circuit at the contacts 13-14 and 13a 14a, as already described.

In Fig. 5, the conductors 24a-25a are connected as described to one phaseand the neutral return or ground wire of a three-phase supply circuit 3334- 35. In this case the operation of the limiter is the same, but it will be noted that the circuit is proof against tampering such as an attempt to short circuit the limiter and'pre vent its operation. 7 e

What I claim is:

1. A current limiter comprising the following instrumentalities: a base, a plurality of thermostats carried on said base and pairs of contacts carried by said thermostats, with means alining two contacts of a pair so that one will be controlled by one thermostat and the otherby another thermostat. g

2. A current limiter comprising the following instrumentalities: a base, an adjustable support attached tosaidbase,

a. thermostatic bar attached to said support, a contact carried on said bar, a second support carried on said base, a second thermostatic bar secured on said support, and a second contact cooperating therewith.

3. A current limiter comprising the following instrumentalities: a pair of thermostatic bars, a pair of contacts carried thereby, means to heat said bars electrically by current passing through said contacts, a pair of spring supports carrying a pair of companion contacts, normally resting under tension of the springs upon the bar contacts, and mechanical means connecting said bars and said springs whereby movement of the thermostatic bars in one direction will raise said springs and cause them to open the contacts, and motion of the bars in the reverse direction will pull down said springs and cause them to again close the contacts, together with a rocking chair for each thermostatic bar, with means to adjust said chairs and means to lock the same when adjusted.

4. A current limiter comprising the following instrumentalities: a pair of thermostatic bars, a pair of contacts carried thereby, means to heat said bars electrically by current passing through said contacts, a pair of spring supports carrying a pair of companion contacts, normally resting under tension or the springs upon the bar contacts, and mechanical means connecting said bars and said springs whereby movement of the thermostatic bars in one direction will raise said springs and cause them to open the contacts, and motion of the bars in the reverse direction will pull down said springs and cause them to again close the contacts, together with mechanical means for adjusting each thermostatic bar, and independent automatic means for adlusting each 0! said springs to compensate for changes in atmospheric temperature.

5. A current limiter comprising the following instrumentalities: a base, a plurality of thermostats carried on said base and pairs of contacts carried by said thermostats, with means aligning two contacts of a pair so that one will be controlled by one thermostat and the other by another thermostat, together with electrical heating means for one of said thermostats, the the other thermostat being responsive to changes DAVID L. KEISER. 

